Apparatus for assembling electrodes



APPARATUS FOR ASSEMBLING ELECTRODES Original Filed Dec. 22. 1959 i; 3a 52e Qil'lu; w 38 w. 42-

43 v Y \\`1\ G 9 v l ff 4.4. i INVENTOR @go/Q65 A. FREEMAN BYy-lbul V 3,110,994 APPARATUS FOR ASSEMBLING ELECTRQDES George A. Freeman, East range, NJ., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvia Original application Dec. 22, 1959, Ser. No. 361,339. Dlvided and this application Dec. 2, 1960, Ser. No. 73,387 2 Claims. (Cl. 29-227) This invention relates to a thermionic electrode for an an electric discharge device and, more particularly, to apparatus for assembling such electrodes and is a division of copending application, Serial No. 861,339, led December 22, 1959, entitled Electrode Component and Process and Apparatus for Assembling Electrodes.

Recently there has been marketed in this country an improved thermionic electrode for high pressure mercury vapor (HPMV) lamps that markedly increases both the useful life and lumen maintenance of such lamps by providing a reservoir of electron-emissive material that is shielded from the gaseous discharge and the erosive effect thereof. This is accomplished byV depositing the emission material by means of a dip process between the spaced intermediate turn or turns of a refractory Wire coil that has closed end sections and is mounted on a suitable core member such as a tungsten rod. A tightly wound outer coil is then threaded over and interlocked with the inner coil thereby enclosing the expanded medial section thereof and the reservoir of emission material therein. The emission material is thus protected from the arc and the sputtering of such material onto the bulb surface and the progressive blackening thereof is inhibited.

As presently manufactured the inner coil and core member are dimensioned to be locked together by means of a force fit. However, since the inner coil must be tightly fitted onto the rod to permit the outer coil to be threaded over the inner coil and locked therewith without displacing the latter, it frequently happened that the expanded medial section of the inner coil partially collapsed and became permanently distorted as the rod was being inserted. When this occurred the inner coil had to be discarded since the spacing between turns of the expanded section thereof was decreased andsaid section thus could not hold or accommodate the required amount of emissionv material. Narr-owing the diameter tolerances of the rod and inner coil as much as practical to minimize the compressive stress on the inner coil and prevent the expanded medial section from collapsing during assembly failed to solve this problem.

It is accordingly the general object of the present invention to overcome the foregoing and other problems associated with the assembly and use of composite thermionic electrodes of the aforesaid character.

Another object is the provision of apparatus which will enable the core member and inner coil to be assembled with a minimum amount of labor and shrinkage.

A further and more specic object is the provision of an assembling tool for holding the inner coil in such a manner that the core rod can be quickly and conveniently inserted therein without compressing or deforming the ex panded medial section of the coil.

The aforesaid objects of the invention, and others which will become apparent as the description proceeds, are achieved by providing a holder that is adapted to receive the inner coil and prevent it from turning or being displaced in an axial direction7 without constricting it or Vobstructing access to its interior. The coil is preferably provided with a protruding uncoiled end segment which drops into and becomes interlocked with a groove'in the face of the holder. A coil of this design 3,110-,94 Patented Nov. 12, 1963 is disclosed and claimed in copending divisional application Serial No. 73,386, filed December 2, 1960, and entitled Electrode and Component Therefor. Holding the coil in this fashion permits the rod to be inserted without collapsing the expanded medial section of the coil, especially if the rod is concurrently rotated at a predetermined rate of speed and in a predetermined direction in the manner disclosed and claimed in the aforesaid copending parent application Serial No. 861,339.

A better understanding of the invention and the manner in which the aforementioned objectives are achieved will be obtained by referring to the accompanying drawing wherein:

FIG. 1 is a side elevational view on a reduced scale of an arc tube for a HPMV lamp which incorporates the aforesaid composite type thermionic electrodes and special inner coil component;

FIG. 2 is an enlarged side elevational View, partly broken away and in section, of one of the electrodes of the arc tube shown in FIG. 1;

FIG. 3 is an end View of the arc-supporting portion of the electrode illustrated in FIG. 2;

FIGS. 4 and 5 are side elevational views of the inner coil before and after the coil legs have been trimmed, respectively;

FIG. 6 is a side elevational View of :another type of inner coil;

FIG. 7 is a plan View of a preferred form of coil holder according to this invention;

FIG. 8 is a cross-sectional yView of the holder taken along the line VIH-VIII of FIG. 7, in the direction of the arrows;

FG. 9 is a plan view of the coil holder corresponding to the View shown in FIG. 7 but with the inner coil illustrated in HG. 5 inserted into the holder yand locked in keyed relation therewith;

FIG. 10 is a cross-sectional view of the holder and inserted coil taken along the line X--X of FIG. 9, in the direction of the arrows; and

FIG. l1 is a side-sectional view of the coil and holder similar to the view shown in FIG. 10 but with the core rod in its inserted position preparatory to the withdrawal of tlhe rod-.and-coil assembly from the holder.

While the present invention can be advantageously employed in assembling various kinds of structures wherein one member is force-fitted into another member that is susceptible to distortion when compressively stressed, it has particular utility in connection with the 'assembly of composite thermionic electrodes for HPMV lamps and has accordingly been so illustrated and will be so described.

With specific reference to the form of the invention shown in the drawing, in FIG. 1 there is shown an arc tube 12 for a HPMV lamp comprising a tubular envelope 14 of quartz or the like that is closed at each end by a press seal 16. A pair of oppositely disposed thermionic electrodes 2li are anchored in each of the seals 16 and electrically connect with the usual ribbon-conductor assemblies 13 which are hermetically embedded in and extend through the aforesaid seals. A filling of ionizable starting gas -such as argon or the like is also sealed within the envelope 14 along with a charge of mercury 13 and an auxiliary electrode 21 that is disposed adjacent one of the main electrodes 2.1il and electrically connects with a separate ribbon-conductor assembly 19.

As shown more particularly in FIGS. 2 and 3, each of the main electrodes 2G consists generally of an outer coil 24 and an inner coil 26 of linear configuration, and a core member such as a cylindrical tungsten rod 22 that is inserted into and locked by means of a force fit with the inner coil. Both the outer coil 24 and the inner coil 26 are ofsubstantially uniform diameter and are wound from refractory metal wire such as tungsten for example. The outer coil 24 is tightly wound so as to form a closed helix and is threaded over and interlocked with the inner coil 26, the end turns whereof are'also tightly wound and constitute closed end sections. The intermediate turns 28 of the inner coil 26 are spaced a predetermined distance from each other and from the adjacent end turns and constitute an expanded medial section that is filled with a predetermined amount of suitable electron-emis- Vsive material 30 such as the Well-known alkaline earth carbonates, thoria, etc., or mixtures thereof. The emission material 39 is preferably applied by mixing it with a suitable binder to form a slurry and dipping the rodand-inner soil assembly therein. Upon hardening the emission material Ifirmly adheres to and bridges the intermediate turns 28 thereby filling the expanded medial section of the coil as shown. The end of the rod 22 opposite the aforesaid coils is preferably shaped .to provide a hat end section 21 in order to facilitate the electrical connection thereof with the ribbon-conductor assembly 13 and its subsequent embedment in the press seal 16. The aforesaid inner and outer coils are also located a predetermined distance inward from the cylindrical end of the core rod 22 as shown.

The present invention relates to a novel apparatus for assembling composite type electrodes of the aforesaid character rather than to such electrodes per se and this apparatus will now be described.

As is disclosed and claimed in theraforesaid copending parent application Serial No. 861,339, the assembly of the rod 22 and inner coil 26 can be very quickly and conveniently achieved by concurrently rotating and inserting the rod into the coil while the latter is held in such a manner that displacement thereof in both an axial and radial direction is prevented, Without obstructing the entrance of or access to the interior of the coil along a path coincident with thelongitudinal axis thereof. A preferred apparatus for holding the inner coil 26 during the assembly thereof with the rod 22 in accordance with the foregoing procedure is illustrated in FIGS. 7 and 8. As there shown, the holder `comprises a rigid support member such as a metal block having a major cavity 3S that extends inwardly from its upper face and merges with a minor cavity that opens into and coaxially extends from the bottom of said major cavity. Both of the aforesaid cavities are of cylindrical configuration, the major cavity being at least as long as but slightly larger in diameter than the outside diameter of the inner coil 26, as for example .-010 of an inch in the case of a 1000 watt coil that has an outside diameter of approximately .149 of an inch.

- The minor cavity B is slightly larger than the diameter of the rod 22 and has a length equal to the distance between the cylindrical end of the rod 22 and the koutermost turn 32 of the inner coil 26, when the latter is locked in its positionof use on said rod.

Due to the dierence in diameter of the aforesaid major and minor cavities there is provided an inwardly protruding annular shoulder 41 at the bottom of the major cavity 3S which is adapted by virtue of its location to serve as a stop for the inner coil 26 when the latter is placed into lthe holder as set forth below. A recess such as a groove 39 is provided in the upper face of the support member 36 which groove communicates with and extends tangentially from the major cavity 38, as shown most particularly in FIG. 7. By virtue of its dimensions and special'coniiguration the support member 36 is able to receive and immobilize the inner coil 26 in the required manner, as -will be described below.

As shown in FIG. 4, the inner coil 26 as wound has a leg 31 at each end which protrude at substantially right angles from the same side of the coil. In accordance with the invention claimed in lthe aforesaid copending divisional application Serial No. 73,386, one of said legs is severed at a point located a predetermined distance from the coil body. Thus, vat least one of the end turns of the inner coil 26 is terminated by a substantially straight end segment 34 that protrudes laterally from the outer surface of the coil body and constitutes a tangential extension of the aforesaid end turn, as illustrated in FIGS. 2, 3 and 5. This segment is of such a length that it projects beyond the outer `surface of the coil ia distance at least equivalent to the diameter of the wire from which the inner coil is wound and preferably about twice the Wire diameter, as is disclosed in the aforesaid copending divisional application. As illustrated in FIG. 6, by cutting the coil leg 31 at the opposite end of the coil in a direction normal rather than parallel to the longitudinal axis of the coil, an inner coil 26a having an end turn 32a that is tapered rather than terminaed abruply may also be provided.

As shown in FIGS. 8 to ll, the depth of the groove 39 in the upper face of the holder is at least equivalent to the diameter of the wire from which the inner coil 26 is wound and said groove is of suicient length to accommodate the uncoiled end segment 34. The minor cavity il may be Vented to the atmosphere as by a passageway .32 that extends from the bottom thereof to the proximate face of the support member 36.

As will be noted from FIGS. 10 and ll, the axial distance between the bottom of the groove 39 and the annular shoulder 41 is substantially equal to the distance between the uncoiled end segment 34 of the coil 26 and the opposite end of the coil. Thus, when the coil is inserted into the holder both ends of the coil are engaged and supported by the holder. To assemble the rod 22 with the inner coil 26 the end of the coil opposite the end with the uncoiled end segment 34 is inserted into the support member 36 and the coil rotated untilV the protruding end segment 34 falls into the groove 39. The inner coil 26 is thus locked or keyed with the support member 36 and prevented from turning and is seated against and supported by the annular shoulder 41 at the bottom of the major cavity 38, as shown in FIGS. 9 and 10. The core rod 22 is then concurrently rotated about its oWn axis and inserted into the inner coil 26 along a path coincident with the longitudinal axis thereof, as is shown in FIG. 11 and described in detail in the aforesaid copending parent application Serial No. 861,339, thereby enabling the rod to be inserted with a minimum of pressure on the expanded medial section yof the coil. The axial thrust on the rod 22 is continued until the cylindrical end thereof seats against the bottom 43 of the minor cavity 40 and the inner coil 26 is thus precisely located in its position of use on the rod. Rotation of the rod is then stopped and the rod-and-coil assembly withdrawn from the support member 35 and the subsequent operations required to complete the fabrication of the electrode 20 are carried out.

It has been found that by assembling the rod 22 and inner coil 26 in the foregoing manner the shrinkage due to distorted coils during rod insertion surprisingly dropped from about 25% and higher to less than 2%.

It will be apparent that the inner coil 26 can be prevented from turning Within the holder by means other than the above-mentioned combination of an interlocking groove 39 and uncoiled end segment 34. For example the end of the square cut end turn 32 could be engaged and the coil thus prevented from turning Vby means of a suitable stop that projects either from the annular shoulder 41 or the side Wall of the majorcavity 38, in ywhich case the aforesaid uncoiled end segment or groove Would not be required. However, the groove-and-segment design is preferred insofar as it not only prevents the coil from rotating but enables the holder to support the uppermost end thereof and thus absorb, so to speak, pressure that would otherwise be exerted on and possibly deform the expanded medial section of the coil.

It will be recognized from the foregoing that the objects of the invention have been achieved by providing a device for holding the inner coil in such a manner that it can be quickly and conveniently assembled with the core member Without being deformed or distorted.

While a preferred embodiment has been illustrated and described, it is to be understood that various modications can be made therein Without departing from the spirit and scope of this invention.

I claim: Y

1. An assembling tool for holding an elongated wire coil of substantially uniform outside diameter that has a collapsible medial section and an end turn terminated by an uncoiled substantially straight end segment that projects tangentially beyond the body of said coil, said tool comprising a rigid support member having; (l) a major cavity therein of `cylindrical configuration that extends inwardly from one end of said support member and is slightly larger in `diameter than the outside diameter of said coil, (2) a minor cavity of cylindrical contiguration and predetermined length that extends coaxially from the bottom of and merges with said major cavity, (3) an annular shoulder at the bottom of said major cavity that protrudes a considerable distance inwardly into said major cavity and is thus adapted to serve as a stop for said coil, and (4) a groove in the end face of said support mem- -ber extending tangentially from and communicating with said major cavity; said groove having a length and depth at least equal to `the corresponding dimensions of the protruding uncoiled end segment of the coil; and the axial distance between said shoulder and the bottom of said groove being substantially equal to the distance between said nncoiled end segment and the opposite end of said coil.

2. An assembling tool for holding an elongated wire coil as set forth in claim 1 wherein said support member comprises a metal block the :closed end whereof is Vented by means of a passageway that extends from the minor cavity to the outer surface of said block.

References Cited in the file of this patent UNITED STATES PATENTS 987,238 Kersten Mar. 21, 1911 1,451,708 Mitchell Apr. 17, 1923 2,331,920 McMaster Oct. 19, 1943 2,400,548 Geertsema May 21, 1946 2,691,143 Lawson Oct. 5, 1954 

1. AN ASSEMBLING TOOL FOR HOLDING AN ELONGATED WIRE COIL OF SUBSTANTIALLY UNIFORM OUTSIDE DIAMETER THAT HAS A COLLAPSIBLE MEDIAL SECTION AND AN END TURN TERMINATED BY AN UNCOILED SUBSTANTIALLY STRAIGHT END SEGMENT THAT PROJECTS TANGENTIALLY BEYOND THE BODY OF SAID COIL, SAID TOOL COMPRISING A RIGID SUPPORT MEMBER HAVING; (1) A MAJOR CAVITY THEREIN OF CYLINDRICAL CONFIGURATION THAT EXTENDS INWARDLY FROM ONE END OF SAID SUPPORT MEMBER AND IS SLIGHTLY LARGER IN DIAMETER THAN THE OUTSIDE DIAMETER OF SAID COIL, (2) A MINOR CAVITY OF CYLINDRICAL CONFIGURATION AND PREDETERMINED LENGTH THAT EXTENDS COAXIALLY FROM THE BOTTOM OF AND MERGES WITH SAID MAJOR CAVITY, (3) AN ANNULAR SHOULDER AT THE BOTTOM OF SAID MAJOR CAVITY THAT PROTRUDES A CONSIDERABLE DISTANCE INWARDLY INTO SAID MAJOR CAVITY AND IS THUS ADAPTED TO SERVE AS A STOP FOR SAID COIL, AND (4) A GROOVE IN THE END FACE OF SAID SUPPORT MEMBER EXTENDING TANGENTIALLY FROM AND COMMUNICATING WITH SAID MAJOR CAVITY; SAID GROOVE HAVING A LENGTH AND DEPTH AT LEAST EQUAL TO THE CORRESPONDING DIMENSIONS OF THE PROTRUDING UNCOILED END SEGMENT OF THE COIL; AND THE AXIAL DISTANCE BETWEEN SAID SHOULDER AND THE BOTTOM OF SAID GROOVE BEING SUBSTANTIALLY EQUAL TO THE DISTANCE BETWEEN SAID UNCOILED END SEGMENT AND THE OPPOSITE END OF SAID COIL. 